並列タイトル等III-窒化物半導体縦型構造UVC LED作成のためのMOVPE成長及びレーザーリフトオフプロセスに関する研究
一般注記Metal organic vapor phase epitaxy (MOVPE) growth and laser lift-off (LLO) process of UVC material systems for in use of fabrication of III-nitride vertical UVC LEDs are studied. This study demonstrates that LLO can be achieved using GaN/AlXGa1-XN based strained superlattice layers to enable fabrication of vertical UVC LEDs in the future. As part of this study, a review of current work on DUV LLO, UVC LLO processing and challenges, and MOVPE growth of UVC material systems are discussed. Experimental results demonstrating full 2” wafer LLO are presented in detail. Growth of III-V nitride UVC material systems is quite challenging, making growth optimizations necessary starting with tool and growth method selection. Comparing several types of reactors, a horizontal flow reactor with low rotation speed demonstrated the best thickness uniformity of 8.2%. Pulsed growth at 1100ºC and 10 kPa with high V/III ratio was selected, due to demonstrating the highest growth rate and crystal quality. FWHMs of (0002) and (10-12) are 309.6 and 617 arcsec, respectively, in this growth. Laser etch rate, using a 248 nm KrF laser dosage of 1 J/cm2 and 38 ns pulse width, was determined to be 10nm per burst on GaN. A 20 pair GaN/Al0.7Ga0.3N (2/5 nm) strained layer superlattice was employed to absorb the UV laser during the LLO process and suppress the dislocations from climbing to the UVC LED epitaxial structure. 2 nm thick GaN layers were grown and sandwiched between Al0.7Ga0.3N to try to compensate for strain to match the lattice parameters of the n-Al0.7Ga0.3N. No crystal degradation occurred as a result of the introduction of the SLS into various epitaxial structures as confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. Furthermore, there is no evidence of cracking or damage observed as a result of LLO processing, as confirmed by SEM and transmission electron microscopy (TEM) analysis. Lateral LED devices using wafers grown with the SLS exhibited 252, 258 and 266nm emission, confirming that the superlattice will not inhibit the ability to grow UVC LEDs. Vertical device emission was not observed and may be caused by the heating at the metal interface causing delamination or copper migration shorting the LED device as shown by secondary ion mass spectroscopy (SIMS) analysis. If the n-layers are increased to approximately 2 μm, catastrophic heating could be avoided. Side wall passivation could be employed to prevent migration and shorting caused by the copper. Successful growth of UVC LED structure and LLO of a 2” sapphire substrate was accomplished without any cracking or use of UVC incompatible materials. Growth of a highquality UVC LED epitaxy was confirmed by x-ray diffraction and transmission electron microscopy (TEM) analysis. TEM also revealed a single pair of the GaN/ Al0.7Ga0.3N SLS was sufficient to allow LLO without damage to the MQW. These achievements represent a significant step in the volume of knowledge to help achieve vertical UVC LEDs fabrication it is an early work capable of demonstrating full wafer LLO of a UVC based material system.
2017
コレクション（個別）国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
受理日（W3CDTF）2017-12-04T02:02:48+09:00
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